In a vehicle fitted with a manual transmission, minimization of fuel consumption with respect to vehicle emissions by means of an appropriate combustion engine operating point, requires that the driver shifts gear at the right time.
Methods to determine and display an optimized shift point on the instrument panel are already known. It is known from U.S. Pat. No. 4,555,691 how to define or determine the shift point through reaching an engine speed threshold and a vehicle speed. Patent specification U.S. Pat. No. 4,539,868 describes a method wherein the current engine operating point, characterized by the load and engine speed, is first calculated. This operating point is set in the engine consumption map, whence a comparison is made with the optimum consumption. If better consumption is possible, a lamp on the instrument panel is switched on. A similar method is known from DE 31 28 080 A1, wherein the control system, after comparing the operating data with a stored consumption map, passes a signal to a gear shift indicator if the stored limit values are selected so that, when the limit values at the driven wheels are exceeded, at least equally high tractive power is available in the next higher gear with a larger throttle opening.
The disadvantage of the known methods is mainly the relatively high expenditure on calibration, which is needed to store a consumption map in the control system.